1. Field of the Invention
The present invention relates to control of ultraviolet lamps, primarily in a dry film curing machine, and provides for precise control of such lamps to insure that they provide a constant desired light intensity at various set levels.
2. Description of the Prior Art
Dry film curing machines are well known, and utilize open mesh belts that carry a film past heaters. Generally these heaters have been infrared heaters for heating the film to a desired level and insuring that the moisture content is reduced sufficiently for use. The dry film curing machine shown schematically herein is well known, and, also, ultraviolet lamps have been known for providing heat to various film drying processes. However, controlling the intensity of ultraviolet lamps is very important, and obtaining automatic controls that are accurate and reliable has been difficult. One primary problem is that conventional sensors are inaccurate. The ultraviolet lamps are elongated, and an arc is formed inside a quartz envelope. The lamp will bow between its supported ends as the temperature of the lamps changes, and the arc also bends and shifts from its start position. Providing a light sensor that will accurately indicate the intensity of the arc even as the arc shifts, has not been achieved.
It has been known that the intensity of ultraviolet lights can be controlled by controlling the power to the lamp and manual power controls have been utilized which adjust the power level up to compensate for lamp aging. The voltage to the lamp has to be maintained above a fairly high level, so the control is primarily a current control.
Another problem occurs, however, when the lamps are being cooled, and the current of the lamps is reduced, the cooling effect may cause the voltage across the lamp to drop significantly. If the voltage drops too far, the lamp power controller will go into its "start" mode automatically, causing a high current surge. Thus there has to be a desirable control of the cooling fan to make sure that the operating voltage is maintained within a reasonable range. If the lamp gets too hot, of course, it is subject to damage, so a fan is necessary.
The present invention provides for controls to make the use of ultraviolets lights possible because of the accurate control of the intensity level of the ultraviolet (UV) lights, as well as providing controls which insure that the cooling for the lamps is not excessive when they are operating at low set intensities.